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HOME> Expert Assessments>Hazards Outlook

U.S. Hazards Outlook - Made June 27, 2017

 Days 3-7Days 8-14Prob. Days 8-14
Precipitation No HazardsNot Available
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Categorical Outlooks
Experimental Probabilistic Outlooks (Information)

Valid Friday June 30, 2017 to Tuesday July 11, 2017

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT June 27 2017

Synopsis: A couple of low pressure systems are expected to progress east along a nearly stationary front extending across the Great Lakes, Midwest, and central Great Plains during the next week. An area of upper-level high pressure is forecast to build over the high Plains by the 4th of July and then expand east during Week-2. Hurricane Dora in the east Pacific is forecast to weaken as it tracks near the 20th parallel prior to this period. An area of upper-level high pressure is expected to persist over eastern mainland Alaska through the first week of July.

Hazards Detailed Summary

For Friday June 30 - Tuesday July 04: Heavy rainfall and flash flooding remain the primary concerns across the central U.S. this week, followed by an increasing risk of a heat wave during early July. Model guidance remains consistent that abundant low-level moisture will develop across much of the eastern and central U.S. with the deterministic 6Z GFS model indicating precipitable water values increasing to more than 1.75 inches, focused along a front. Heavy rainfall (1 to 3 inches, locally more) is likely along this front, extending from New England and the Great Lakes southwest to the southern Great Plains on June 30 and July 1. The most likely area for heavy rain is then expected to shift back to the north across the northern/central Great Plains and Midwest on July 2 and 3. The depicted heavy rain hazards are based on the precipitation forecasts from the 6Z GFS and 0Z ECMWF ensemble means. Given the high moisture content of the atmosphere, thunderstorms throughout the central and eastern U.S. will be capable of triggering flash flooding this week. Severe weather, primarily damaging wind and large hail, could also occur in the strongest thunderstorms, but low predictability precludes a designation of a specific severe weather hazard at this time.

An upper-level ridge is expected to strengthen over the high Plains by early next week and begin to expand east across the central U.S. Therefore, much above-normal temperatures (10 degrees F or more) are forecast to affect the northern and central Plains on July 3 and 4. Maximum temperatures are expected to warm well into the 90s to near 100 degrees F by July 4 across this region. This heat is likely to worsen ongoing drought conditions across eastern Montana and the Dakotas.

On June 30 and July 1, a low pressure system with onshore flow is expected to bring heavy rainfall (locally more than 1.5 inch per 24 hours) across Kodiak Island, the southeast Kenai peninsula, and the Prince William Sound. Strong ridging aloft is expected to result in much above-normal temperatures across the Yukon River Valley where maximum temperatures above 85 degrees F are forecast on July 3 and 4.

For Wednesday July 05 - Tuesday July 11: The 6Z GFS and 0Z ECMWF ensemble means agree with an amplified ridge centered over the Great Plains during Week-2. This anomalous ridging supports a slight risk of much above-normal temperatures for parts of the central and eastern U.S. through at least July 10. The outlined slight risk area is generally consistent with the GEFS reforecast tool which features a broad area where maximum temperatures have a 20 to 30 percent chance of exceeding the 85th percentile compared to climatology. Although only a slight risk for much above-normal temperatures is posted, heat index values may exceed 105 degrees F in the more humid areas of the central and eastern U.S. Based on 850-hpa temperatures predicted by the deterministic GFS model, the GEFS calibrated heat index forecast, and climatology, an excessive heat hazard is posted for parts of the central U.S. on July 6 and 7.

A slight risk of much above-normal temperatures is also posted for parts of eastern mainland Alaska through July 9 due to persistent ridging aloft. The deterministic GFS model remains consistent with maximum temperatures warming to near 90 degrees F across the upper Yukon Valley early in Week-2.

An upper-level ridge is forecast to shift slightly north to the Four Corners region which would lead to increased moisture across the desert Southwest. This increasing moisture is expected to result in more convection and a higher risk of flash flooding across Arizona and New Mexico during Week-2.

The U.S. Drought Monitor valid on June 20 shows D2-D4 drought coverage over the CONUS now at 2.13%, a slight increase from 1.57% one week ago. This increase is tied to the emergence of severe drought in the Northern Plains.

Forecaster: Brad Pugh


Click here to see a display of the GFS Ensemble Forecasts

Please consult local NWS Forecast Offices for short range forecasts and region-specific information.